Of all the synthetic polymers considered as materials with useful gas permeation properties, such as resistance to passage of oxygen, carbon dioxide, water, and the like, poly(vinyl alcohol) (PVOH), which is a polymer made up of units of the structure ##STR1## and generally prepared by the total or almost total hydrolysis of homopolymers of vinyl acetate or related vinyl esters, the starting polymer made up of units of the structure ##STR2## where R is alkyl, that is, from one to eight carbon atoms, preferably methyl, ranks as the most impervious to the passage of small molecules. PVOH derives this property from the high cohesive energy density and polarity of the hydroxyl groups. The presence of the network of hydroxyl groups has the concomitant effect of rendering the polymer (PVOH) impermeable to gases, but sensitive to moisture. The strong intermolecular interaction resulting from the high polarity of the --OH functional group gives rise to a melting temperature in the vicinity of the degradation temperature of PVOH. Consequently, melting is accompanied by degradation. The degradation is so severe that PVOH by itself cannot either be melt extruded or injection molded. Co-polymers having a low mol percentage of ethylene, such as from about 5 to about 25 mol percent, are similar to poly(vinyl alcohol) in that they cannot be melt-processed into film without the aid of plasticizers.
In U.S. patent application Ser. No. 07/781,715, filed Oct. 22, 1991, now U.S. Pat. No. 5,189,097 now also European Patent Application 91-311265, filed Dec. 4, 1991, which has some of the same inventors as the present application, are disclosed additive polymers useful in allowing melt processing of the poly(vinyl alcohol) materials discussed above without significant alteration of their physical and barrier properties. These additive polymers are copolymers of lower alkyl methacrylates or acrylates with a variety of nitrogenous monomers, especially those bearing amide groups, and most especially N-vinylpyrrolidone. Further is disclosed as more useful additives terpolymers containing lower alkyl methacrylates or acrylates, the same nitrogenous co-monomers, and copolymerized unsaturated carboxylic acids, such as methacrylic acid. It is further disclosed that these latter terpolymers form segmented copolymers on combining with the poly(vinyl alcohol) matrix polymers under certain processing conditions.
In a patent application in the U.S., Ser. No. 872,478, filed on Apr. 23, 1992, now abandoned also with some of the same inventors as the present application, is disclosed that copolymers of lower alkyl methacrylates and/or acrylates with unsaturated carboxylic acids, such as copolymers of methyl methacrylate with methacrylic acid, are also useful for the same purposes. It is further disclosed that the composites so formed may be segmented copolymers under certain processing conditions.
What has been discovered in the present invention is that certain of these composites of poly(vinyl alcohol), or copolymers which contain at least 50 mol % of ##STR3## units, with lower alkyl methacrylate or acrylate copolymers with at least one of copolymerized acid or amide, especially cyclic amide, functionality, when melt-blended with structural polar polymers, produce blends of excellent physical, optical and barrier properties.
In the applications noted above, it had been found that a polymeric composite comprising from about 40 to about 95 parts, of a first polymer containing at least 50 mol % of units, preferably at least 90 mol %, of the structure ##STR4## and optionally units of the structure ##STR5## where R is H or CH.sub.3, and from 5 to about 60 parts by weight of a second polymer containing at least about 70 parts of units derived from at least one lower alkyl methacrylate or acrylate, (lower alkyl meaning from 1 to 4 carbon atoms such as methyl, ethyl, propyl, or butyl), preferably methyl methacrylate, and at least one of either up to about 25 parts of units derived from a vinyl or vinylidene monomer containing an amide group, preferably a cyclic anide group of units of the structure ##STR6## where n is 2, 3, 4, or 5, preferably units derived from N-vinyl pyrrolidone, or up to about 25 parts of units derived from an unsaturated carboxylic acid or anhydride, preferably methacrylic acid, may be melt-processed, such as by extrusion, into useful objects such as sheet, film, and fiber. It had further been found that combination of the two polymers noted above by melt-mixing will form a segmented melt- processable polymer wherein the two polymers are chemically combined to form a graft copolymer. Lower levels, down to 2 parts, of the additive in the composite may be used when the additive polymer is free from amide functionality or when the composite contains poly(vinyl alcohol) which has been washed or has been neutralized with acid such as phosphoric acid to remove residual sodium acetate, as taught in U.S. Pat. No. 3,425,979.
It is now been found that these composites may be blended, preferably in the melt, with polar polymers, to give a melt- processable blend which may be processed into useful sheet, film, or molded objects. In the sense that processing of the polar polymer is improved, these composites may be considered "processing aids". Polar polymers may be described as polymers which contain functionality other than carbon and hydrogen, and include poly(vinyl halides), such as poly(vinyl chloride) (PVC), poly (vinyl esters), such as poly(vinyl acetate), poly(meth)acrylic esters, polyglutarimides, polymers containing (meth)acrylonitrile, such as styrene/acrylonitrile copolymers or acrylonitrile/butadiene/styrene copolymers (ABS), polyesters, such as poly(alkylene terephthalates), polyamides, ethylene-vinyl alcohol co- and terpolymers, of less than 50 mol % vinyl alcohol units, ethylene-carbon monoxide copolymers, polycarbonates, poly(alkylene oxides), such as poly (propylene oxide) or poly(ethylene oxide), phenoxy resins, such as those formed by the reaction of epichlorohydrin and a bisphenol, and the like. The invention further applies to polar polymers which are of natural origin or modified from polymers of natural origin, such as starch, lignin, chitin, chitosan, cellulose, or chemically modified cellulose, such as esters such as cellulose acetate, cellulose acetate-propionate, cellulose acetate-butyrate, or ethers such as methyl cellulose. Many of these polymers are extremely difficult to process, and may be described as melt-intractable. The ratio of polar polymers to the composites may be from about 10:95 to about 5:90, preferably for thermoplastic polar polymers from about 60:95 to about 5:40, and more preferably from about 80:95 to about 5:20. Particularly useful polar polymers are aliphatic polyamides formed from lactams, such as polycaprolactam, polyundecanolactam, and polydodecanolactam, the polycarbonate formed from bisphenol A, poly(ethylene terephthalate), and elastomeric polyurethanes, such as those with polyether or polyester-polyol segments.